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Silicon Modulator Brings Optical Computing A Step Closer

This electrically driven, compact silicon modulator is based on a photonic crystal design.

Saturday, 01 April 2006

University of Texas at Austin and Omega Optics, Austin, Texas

For decades, silicon has not been considered a favorable material for manipulating light. Electrical Engineering Professor Ray Chen at the University of Texas at Austin and Wei Jiang at Omega Optics in Austin recently developed an electrically driven, compact silicon modulator based on a photonic crystal design that offers significant performance improvements over existing Mach-Zehnder Interferometer (MZI)-based silicon modulators.

A Matrix of Nanometer-Scale Holes is drilled into a photonic crystal waveguide that slows light, improving the modulation capabilities of silicon devices.Chen’s research shows that silicon modulators based on photonic crystal matrixes consume a tenth of the power and have an active device length that is ten times less than commercially available MZI silicon modulators with rib waveguides. As light passes through a hexagonal array of tiny holes drilled into silicon, it slows the light, giving the modulator more time to respond to its electrical drive signals. This helps reduce the amount of current needed to modulate light. To achieve this, the hole size of the photonic crystal must be on the nanometer scale. The reward is one or two orders of magnitude reduction of interaction length and electric current.

Making this device was not straightforward. According to Jiang, “The issue of fabrication is yield, and the key is planarization.” Jiang designed a flattened structure for the photonic crystal after simulating and comparing the optical and electrical performance of a variety of alternative structures. This structure was chosen because it requires a minimum number of processing steps.

The devices may find use in optical computing and communications. The silicon modulator could be used to relay data or information. By varying the electric current, one can change the modulation rate, interval, or the intensity of light to produce different patterns. The team intends to continue the research, improving the silicon modulator by optimizing the electrode design and reducing the contact resistance.

The next innovation would be to make lasers on silicon that convert electricity input into light output. Chen and Jiang feel that the modulator structure will be a baseline platform for such electrically pumped silicon lasers.

This article was written by Ray Chen, the Temple Foundation Endowed Professor at University of Texas Austin, and Wei Jiang of Omega Optics. For more information, contact Mr. Chen at 512-471-7035.